1. Field of the Invention
The present invention relates to a projection-type display device that projects an image outputted from a projection unit onto a screen from behind to display the video.
2. Description of the Background Art
FIG. 10 is a diagram showing the interior of a conventional multi-projector seen from a side. The multi-projector described here includes projection-type display devices (rear projection type video projectors) stacked vertically and laterally to display one large screen. FIG. 10 shows two conventional projection-type display devices 300 stacked vertically. In FIG. 10, the reference numeral 13 denotes a cabinet (the body of the projection-type display device), 2 denotes a projection unit provided in the rear part in the cabinet 13 for projecting an image (output video) forward, 3 denotes a screen provided in the front of the cabinet 13, and 50 denotes an angle-of-view correcting mechanism (an angle-of-view correcting mechanism device) that supports the projection unit 2 in the lower part of the cabinet 13 to adjust the direction of the projection unit 2 to correct the angle of view of the image projected from the projection unit 2 onto the screen 3.
As shown in FIG. 10, the image is projected directly from the backside of the screen 3. In this case, the dimension of the projection-type display device in the depth (front-back) direction X must be set long. FIG. 11 shows projection-type display devices 200 devised to shorten the dimension in the depth direction X. In FIG. 11, the reference numeral 12 denotes a cabinet (the body of the projection-type display device), and 2, 3 and 50 denote the projection unit, screen, and view-of-angle correcting mechanism entirely the same as those shown in FIG. 10.
In the projection-type display device 200, the projection unit 2 is provided in the lower part in the cabinet 12 to project the image upwardly, and the screen 3 is located in the upper front of the cabinet 12. Additionally, it has a reflecting mirror 4 provided in the upper part in the cabinet 12, which receives the image and reflects it toward the screen 3. The angle-of-view correcting mechanism 50 supports the projection unit 2 on the bottom of the cabinet 12, similarly to that shown in FIG. 10.
FIGS. 12 to 14 are conceptual diagrams showing images projected on the screen 3, which show the images shifted off the screen 3. The images are shifted off on the screen 3 due to the following six kinds of deviations and combinations thereof: vertical deviation, lateral deviation, inclination, projecting magnification, vertical trapezoidal distortion, and transverse trapezoidal distortion. In FIG. 12, 51a shows an image projected with insufficient projecting magnification with respect to the screen 3. 51b shows an image projected with an undesired inclination. 51c shows an image projected with vertical and lateral deviation. In FIG. 13, 51d shows an image projected with vertical trapezoidal distortion. In FIG. 14, 51e shows an image projected with transverse trapezoidal distortion.
Conventionally, cathode-ray tubes have chiefly been applied as the projection units 2, which allow easy correction to the deviations on the screen 3 with electric circuitry. With the recent trend toward digitization, however, there is now a growing tendency to mainly use liquid-crystal devices and digital mirror devices (DMD). Since the optical path cannot be electrically corrected with these devices, the projection units 2 necessarily require the angle-of-view correcting mechanisms 50.
FIG. 15 is a diagram showing the appearance of a conventional angle-of-view correcting mechanism 50. In FIG. 15, 50a denotes an up-and-down moving plate that can be moved in the vertical direction Y, 50b denotes a horizontal-rotation moving plate that can be rotated as seen from the vertical direction Y, 50c denotes a right-and-left-inclination moving plate that can be inclined as seen from the front-back direction X, 50d denotes a front-and-back inclination moving plate that can be inclined as seen from the right-left direction Z, 50e denotes a frontward-and-backward moving plate that can be moved in the front-back direction X, and 50f denotes a right-and-left moving plate that can be moved in the right-left direction Z.
Next, operation of the projection-type display device 200 will be described referring to FIGS. 11 to 15. The image projected from the projection unit 2 is reflected at the reflecting mirror 4 and produced on the screen 3. The projecting magnification of the image 51a produced on the screen 3 can be corrected by moving the up-and-down moving plate 50a in the vertical direction Y. The inclination of the image 51b produced on the screen 3 can be corrected by rotating the horizontal-rotation moving plate 50b. The transverse trapezoidal distortion of the image 51e produced on the screen 3 can be corrected by inclining the right-and-left-inclination moving plate 50c. The vertical trapezoidal distortion of the image 51d on the screen 3 can be corrected by inclining the front-and-back-inclination moving plate 50d. The vertical and lateral deviation of the image 51c on the screen 3 can be corrected by moving the forward-and-backward moving plate 50e and the right-and-left moving plate 50f respectively in the front-back direction X and the right-left direction Z
As described above, in the conventional projection-type display device 200 shown in FIG. 11, the angle-of-view correcting mechanism 50 includes as many as six moving plates and has a long dimension in the vertical direction Y. Accordingly, installing the angle-of-view correcting mechanism 50 on the bottom surface of the projection unit 2 requires the cabinet 12 to be shaped in a downwardly extended form. This hinders downsizing of the body of the video projector.
Particularly, with the multi-projector, shown in FIG. 11, the extended part 121 protruding in the lower part of the cabinet 12 is formed to go into the projection-type display device 200 lying immediately below. The projection-type display device 200 underneath contains the reflecting mirror 4. Hence, the extended part 121 must be extended downward along the reflecting mirror 4 in the projection-type display device 200 right below, which requires the projection-type display device 200 right above to be long-sized in the front-back direction X.